Steam drive oil production method



April 21, 1964 P. .1. cLosMANN 3,129,758

STEAM DRIVE OII.. PRODUCTION 4METHOD Filed April 27, 1961 2 Sheets-Sheetl INVENTOR 1 P. J. OLOSMANN IS AGENT April 21, 1964 P. J. cLosMANN STEAMDRIVE on; PRODUCTION METHOD 2 Sheets-Sheet 2 Filed April 27. 1961 FIG. 4

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S AGENT United States Patent O 3,129,758 STEAM BREVE @EL PRODUCTIGNMETHOD Philip I. Ciosrnann, Houston, Tex., assigner to Shell OilQompany, New Yaris, NY., a corporation of Delaware Fiied Apr. 27, 1961,Ser. No. 106,115 4 Claims. {CL 16e-11) This invention relates to amethod for producing oil from underground formations and pertains moreparticularly to a method of flooding a formation in order to recover oiltherefrom which, because of the characteristics of the oil or the statethat is is in, could not be produced by normal oil producing methods.The method of the present invention is especially applicable forhydrocarbon reservoirs where the -injectivity is relatively low, suchfor example as, tar sands.

Iln some regions oil-bearing formations contain an oil whose viscosityor state is such that the oil does not flow from the formation. Attemptshave been made to heat the .formation with varying degrees of success.The use of heaters in a well is not very satisfactory since the heatcannot penetrate a great distance from the well bore. It is oftendifficult to create a steam flood or drive since the steam condenses andcools in the formation to interfere with the further injection of steamthereinto.

It is, therefore, an object of the present invention to provide an oiliield with a series of injection and production wells and to heat a zoneof the oil-bearing formation close to the production wells, as well as azone close to injection wells, in order to reduce the viscosity of theoil moving from an intermediate zone as oil is produced.

Another object of the present invention is to provide a method ofrecovering oil from an underground formation in a manner to preheat azone around the production well in order to open this zone at the startof a steam flood so that an area is created through which oil can bereadily forced.

A further object of the present invention is to provide an oil recoverymethod wherein the production formation is preheated in overlappingflood patterns at two levels which are vertically displaced one from theother so that a vertical ood of heated fluid cleans the maximum areapossible.

Still another object of the present invention is to provide an oilrecovery method wherein interconnecting fractures are formed in theproducing formation prior to heating the formation with steam so thatthe condensate formed in the formation has a chance to drain oi ratherthan ll the fractures and block the entrance of more steam thereinto.

rihese and other objects of this invention will be understood from thefollowing description taken with reference to the drawing, wherein:

yFIGURE 1 is a diagrammatic plan view of super-imposed horizontal floodpatterns at the start of the dual steam injection preheating period ofthe method of the present invention, the shaded area representing theflow pattern of steam being injected into the lowermost portion of theformation; and,

lFIGURES 2, 3 and 4 are longitudinal views taken in cross-section alonglines `2---2, 3 3 and 4-4 of FIG- URE l, diagrammatically illustratingthe input and output wells of the present invention.

The oil recovery method of the present invention contemplates the use ofa plurality of alternately-disposed steam input, condensate output andproduction output wells which penetrate an oil-bearing formation. Themethod comprises establishing communication between the steam inputwells and the oil-bearing formation near the top -thereof and betweenthe condensate removal wells and the same portion of the formation,while at the same time establishing communication between the outputwells 3,129,758 Patented Apr. 21, 1964 ice and their portion of theoil-bearing 4formation at a level lower than that communicating with theinput and condensate wells. In the event that the wells are cased, whichis the normal condition, communication would be established between awell and the desired level of the producing formation 'by means ofperforating the casing. The oil-bearing formation is then horizontallyfractured from the series of input and condensate wells at the upperlevel and from the series of output wells at a lower level. Thefracturing operation is carried out in a manner such that the fracturesat each level are in open communication with each other, but not withthe series of vertically displaced fractures from the other series ofwells. lf desired, the fractures may be propped open with suitablepropping agents in the event that steam pressures are employed which doinot keep the fractures open. Aln the event that any of the fracturesfrom the input wells extend into the production wells, they are sealedoff in the production wells.

Prior to producing the formation, the oil-bearing formation is preheatedadjacent the upper and lower fractures simultaneously with steam beinginjected through some of the input wells and condensate removed from thecondensate wells, while at the same time steam is injected through someof the output wells while removing condensate from other of the outputwells. After preheating the formation from the two levels for apredetermined period, which period depends upon the character of theformation, the number of wells employed, the vertical spacing betweenthe fractures, etc., the injection of steam into the output wells issubsequently discontinued. A downward steam `drive of oil from theoil-bearing formation is now carried out by injecting steam through theinput wells into the upper portion of the oil-bearing formation toproduce the oil downwardly and horizontally into the output wells fromwhich the oil may be recovered in any desired manner well known to theart.

Referring to FIGURE 1 of the drawing, one typical arrangement of -wellsis illustrated wherein wells 2, 4, 6 and l8 are steam input wellsextending to the upper fractured zone of the oil-bearing formation,while wells 10 and 12 are steam input wells, during the preheat period,extending to the lower fractured zone of the formation. After theformation has been preheated and the downward steam drive has beenstarted through input or injection wells 2, 4, 6 and ti, steam input towells 10 and 12 is cut off and the wells 10 and 12 are either closed oropened as production wells from the lower zone.

The condensate removal wells for removing steam condensate from theupper fracture zone of the oil-bearing formation are represented bynumerals 1, 3, 5, 7, 9, 11, 13, 15 and 17. Wells 21, 22, 23, 24, 25 and26 extend to the lower fractured zone of the oil-bearing formation andare employed as condensate removal wells during the preheat period, andas oil production wells after the steam drive has started from the upperfractured formation.

As shown in FIGURE 2, if necessary, the upper fractures 30 which extendfrom the input wells 2 and 6 and from any adjacent condensate wells areclosed off from the production Wells 21, 22 and 23 to prevent steamescaping up the production wells or along the well casing positionedtherein. Steam shutoff may be accomplished by spotting cement 31, 32 and33 adjacent the bore of the wells or outside the well casings thereof.ln a like manner the lower fracture at 34 may be sealed off at the inputwells 2 and 6, as by cement plugs 35 and 36. lf desired, the cementplugs may be positioned in the injection wells just below the fractureat 30.

In FIGURE 3, a series of condensate removal wells 7, 9 and 11 areillustrated in communication with fracture 30 for removing condensateformed therein due to steam injection through wells 2 and 6 of FIGURE 2.In FIG- URE 3 the wells lll and l2 in communication with the lowerfracture 34 are illustrated during the preheat period at which steam isinjected down wells lil and 12 with the condensate in the fracture 34being removed through the production wells 2l, 22 and 23 of FIGURE 2.After the preheat period wells lll and l2 can be converted to productionwells.

In FIGURE 4 the steam input wells d and 8 and the oil production oroutput wells 2d, 2S and 26 are shown as extending into a relativelypermeable zone wherein the downward steam drive of the present methodcan be accomplished without the necessity of fracturiug the formation.

In the present method of oil recovery the wells are preferably drilledin locations selected so that the wells are adapted to provide twooverlapping injection-production patterns, such as tive-spot patterns,at spacing suitable for steam injection and condensate withdrawal atpressures initially greater than the overburden pressure, and atsomewhat reduced pressures later, if desired. Two series of alternatelyspaced Wells are employed, with one series of wells being fracturedhorizontally near the top of the oil-producing formation while the otherseries of wells are fractured horizontally at a lower depth. Inrelatively thin reservoirs the fractures will be located near the topand the bottom of the reservoir. However, in relatively thick reservoirsit may be necessary to carry out the two-level preheat and steam drivemethod of the present invention at varying depths. In a relatively thickreservoir the upper level of heat supply might be placed part way downfrom the top of the reservoir and the lower level part Way up from thebottom. Subsequently, heat which would normally be lost in a two-levelheating process, due to loss above and below the heated central zone,would be useful in improving the mobility of oil in the upper and lowersections of the reservoir.

In the heating stage, the formation interval between thehorizontally-directed fractures is simultaneously heated alonghorizontally extensive planes. In each fracture the rate of steaminjection and condensate withdrawal is preferably controlled to maintaincondensation all along the fracture. The preheating stage of the presentmethod provides a unique and advantageous type of heated reservoir zonein which to conduct a steam drive. The heated zone is generallydiscshaped and is hottest along the top and bottom and coolest in themiddle. The arrangement of the heated zone is such that steam is appliedat substantially equal pressure along the entire area of the top of thezone. After the preheat period, and after the steam has been shut olf tothe lower fracture, steam injected into the upper fracture pushes theoil bank, in which the cooler and more viscous portions are located nearthe center of the reservoir formation through which the oil bank isdriven. As the steam drive moves the oil bank, the cooler portion of theoil bank is heated primarily by contact with the hotter reservoirformation section around the lower fracture into which the oil bank ispushed. The elevated temperature of the portion of the oil-bearingformation adjacent the upper fracture is maintained by heat from thesteam.

When the formation between the vertically-displaced fractures has beenheated the desired amount, the injection of steam into the lowerfracture is terminated and the steam pressure reduced, causing an insitu regeneration of steam in a manner enhancing the downwarddisplacement of the heated reservoir oil. As the pressure in the lowerfracture is reduced, formation water, as well as condensed steam whichpermeated the roof of the lower fracture, will be vaporized and willdisplace oil toward wells opening into the region of the lower fracture,i.e., the production wells. If part of the oil-bearing formation liesbelow the lower fracture, part of its oil should be produced by thismechanism. After the vertically downward displacement from upper levelto lower level is concluded, release of pressure at the upper levelwould tend to produce some of the heated oil above the central zone byvaporization of water within that region. Thus, the overall economy ofthe process would be enhanced. In most cases the use of fracturepropping agents is not necessary as during the heating stage thefractures can be held open by steam pressure. By the end of thepreheating stage, the sand in the vicinity of the fractures is generallystripped free of enough oil to provide zones of high fluid permeabilityaround the fractures in the Wells. ln some cases it may be desirable toemploy propping agents in the fractures, especially when the overburdenpressure is too great for the fractures to be held open with steampressure.

I claim as my invention:

l. A method of recovering oil from an underground oil-bearing formationwhich is penetrated by a plurality of alternately-disposed wells whichmay be divided into steam-input wells, condensate-removal wells andoil-output wells, said method comprising establishing communicationbetween both the input wells and the condensate removal Wells with theoil-bearing formation at one level thereof, establishing communicationbetween the oil output wells and the oil-bearing formation at a levelSubstantially below that of the other wells, horizontally fracturing theoil-bearing formation from said input and condensate removal wells atone level of the oil-producing formation and in a manner such that thefractures are in open communication with each other, horizontallyfracturing the oil-bearing formation from oil outlet wells at a lowerlevel than said first fracture and in a manner such that the lowerhorizontal fractures are in open communication with each other,continuously injecting steam through said input wells while continuouslyremoving condensate from the condensate removal wells and injectingsteam through some of the oil outlet wells while removing condensatefrom other of the oil outlet wells for a time sufficient to preheat thezone of said oil-bearing formation between the upper and lowerfractures, subsequently discontinuing the injection of steam into theoil output wells, injecting steam into the upper portion of saidoilbearing formation through said input wells to produce oil by adownward steam drive to said oil output wells, and recovering saidproduced oil from said oil output wells.

2. A method of recovering oil from an underground oil-bearing formationwhich is penetrated by a plurality of alternately-disposed wells whichmay be divided into steam-input wells, condensate-removal wells andoil-output wells, said method comprising establishing communicationbetween both the input wells and the condensate removal wells with theoil-bearing formation at one level thereof, establishing communicationbetween the oil output wells and the oil-bearing formation at a levelsubstantially below that of the other wells, horizontally fracturing theoil-bearing formation from said input and condensate removal wells atone level of the oil-producing formation and in a manner such that thefractures are in open communication with each other, horizontallyfracturing the oil-bearing formation from oil outlet wells at a lowerlevel than said first fracture and in a manner such that the lowerhorizontal fractures are in open communication with each other,continuously injecting steam through said plurality of input wells whilecontinuously remov-ing condensate from the condensate removal wells andinjecting steam through some of the oil outlet wells while removingcondensate from the other of the oil outlet wells to preheat the lowerzone of said oil-bearing formation between the upper and lowerfractures, the wells having steam injected into them being spaced in theoil field so that the producing formation is preheated -in alternatehigh and low overlappingg flood patterns extending from said pluralityof wells having steam injected into them at the two frarcture levels,subsequently discontinuing the injection of steam into the oil outputwells, injecting steam into the upper portion of said oil-bearingformation through said input wells to produce oil by a downward steamdrive to said oil output wells, and recovering said produced oil fromsaid oil output wells.

3. A method of recovering oil from an underground oil-bearing formationwhich is penetrated by a plurality of alternately-disposed wells whichmay be divided into steam-input wells, condensate-removal wells andoil-output wells, said method comprising establishing communicationbetween both the input Wells and the condensate removal wells with theoil-bearing formation near the top thereof, establishing communicationbetween the oil output wells and the oil-bearing formation at a levelsubstantially below that of the other wells, horizontally fracturinglthe oil-bearing formation from said input and condensate removal Wellsat a level near the top of the oilproducing formation and in a mannersuch that the fractures are in open communication with each other,horizontally fracturing the oil-bearing formation from oil outlet wellsat a lower level than said rst fracture and in a manner such that thelower horizontal fractures are in open communication with each other,sealing off in the production wells any fractures which may extend froman input or condensate removal well, continuously injecting steamthrough said input wells while continuously removing condensate from thecondensate removal wells and injecting steam through some of the oiloutlet wells while removing condensate from other of the oil outletwells to preheat the lower zone of said oil-bearing formation betweenthe upper and lower fractures, subsequently discontinuing the injectionof steam into the oil output wells, injecting steam into the upperportion of said oil-bearing formation through some of said input wellsto produce oil by a downward steam drive to said oil output wells, andrecovering said produced oil from said oil output wells.

4. The method of claim 3 including the step of propping the fracturesopen.

References Cited in the file of this patent UNITED STATES PATENTS2,813,583 Marx et al. Nov. 19, 1957 2,946,382 Tek et al. July 26, 19603,010,707 Craighead et al. Nov. 28, 1961

1. A METHOD OF RECOVERING OIL FROM AN UNDERGROUND OIL-BEARING FORMATIONWHICH IS PENETRATED BY A PLURALITY OF ALTERNATELY-DISPOSED WELLS WHICHMAY BE DIVIDED INTO STEAM-INPUT WELLS, CONDENSATE-REMOVAL WELLS ANDOIL-OUTPUT WELLS, SAID METHOD COMPRISING ESTABLISHING COMMUNICATIONBETWEEN BOTH THE INPUT WELLS AND THE CONDENSATE REMOVAL WELLS WITH THEOIL-BEARING FORMATION AT ONE LEVEL THEREOF, ESTABLISHING COMMUNICATIONBETWEEN THE OIL OUTPUT WELLS AND THE OIL-BEARING FORMATION AT A LEVELSUBSTANTIALLY BELOW THAT OF THE OTHER WELLS, HORIZONTALLY FRACTURING THEOIL-BEARING FORMATION FROM SAID INPUT AND CONDENSATE REMOVAL WELLS ATONE LEVEL OF THE OIL-PRODUCING FORMATION AND IN A MANNER SUCH THAT THEEFRACTURE ARE IN OPEN COMMUNICATION WITH EACH OTHER, HORIZONTALLYFRACTURING THE OIL-BEARING FORMATION FROM OIL OUTLET WELLS AT A LOWERLEVEL THAN SAID FIRST FRACTURE AND IN A MANNER SUCH THAT THE LOWERHORIZONTAL FRACTURES ARE IN OPEN COMMUNICATION WITH EACH OTHER,CONTINUOUSLY INJECTING STEAM THROUGH SAID INPUT WELLS WHILE CONTINUOUSLYREMOVING CONDENSATE FROM THE CONDENSATE REMOVAL WELLS AND INJECTINGSTEAM THROUGH SOME OF THE OIL OUTLET WELLS WHILE REMOVING CONDENSATEFROM OTHER OF THE OIL OUTLET WELLS FOR A TIME SUFFICIENT TO PREHEAT THEZONE OF SAID OIL-BEARING FORMATION BETWEEN THE UPPER AND LOWERFRACTURES, SUBSEQUENTLY DISCONTINUING THE INJECTION OF STEAM INTO THEOIL OUTPUT WELLS, INJECTING STEAM INTO THE UPPER PORTION OF SAIDOILBEARINGS FORMATION THROUGH SAID INPUT WELLS TO PRODUCE OIL BY ADOWNWARD STEAM DRIVE TO SAID OIL OUTPUT WELL, AND RECOVERING SAIDPRODUCED OIL FROM SAID OIL OUTPUT WELLS.